Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. In addition to petrochemical feed stocks synthesis methods, starchy materials, as well as cellulose materials, may be converted to ethanol by fermentation. Fermentation methods are typically employed for production of consumable ethanol, although the ethanol thus produced may also be suitable for fuels. Fermentation of starchy or cellulose materials also competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acid, e.g., acetic acid, other compounds are formed with ethanol or are formed in side reactions. As examples, esters and/or acetals, e.g., diethyl acetal, may be formed via these side reactions. These impurities 1) limit the production of ethanol; and 2) impede the purification of the ethanol in the crude reaction product. Typically, the separation of esters and acetals from ethanol has proven to necessitate excessive resource requirements, e.g., high energy and/or large numbers of trays.
In view of these shortcomings, a need remains for improved separation schemes, which provide the ability to more effectively separate impurities from ethanol.